1. Field of Invention
The present invention relates to liquid crystal display devices and electronic apparatuses. More specifically, the invention relates to a transflective liquid crystal display device which performs high-contrast display in a transmissive mode.
2. Description of Related Art
Since reflective liquid crystal display devices are not equipped with a light source, such as a backlight, and thus consume less power, they are used in the related art for a variety of portable electronic apparatuses, display units of other apparatuses serving as ancillary equipment, and so forth.
However, since they perform display by utilizing external light, such as natural light or illumination light, they surfer from the problem of poor visibility of the display in dark places. To address or solve this problem, another related art liquid crystal display device uses external light in bright places in the same fashion as the usual reflective liquid crystal display device, and uses an internal light source in dark places so as to achieve highly visible display. That is, this liquid crystal display device combines reflective display type and transmissive display type, and by switching the display type between a reflective mode and a transmissive mode in accordance with the brightness of the ambient light, produces clear display even in a dark environment while reducing power consumption. In this specification, the liquid crystal display device of this type is referred to as xe2x80x9ca transflective liquid crystal display devicexe2x80x9d.
In another related art transflective liquid crystal display device, a reflective film which is made from a metal film composed of aluminum or the like, and which has slits for light transmission, is formed on the inner surface of a lower substrate. In this case, light emitted from a backlight disposed on the outer surface of the lower substrate passes through the slits so as to contribute to transmissive display, while light coming from an upper substrate is reflected from the reflective film so as to contribute to reflective display, whereby the reflective film serves as a transflective film.
Although the liquid crystal display device described above can perform highly visible display regardless of the presence of external light, there is a problem in that the display brightness is insufficient in the transmissive mode compared to the reflective mode. A significant reason for this problem is the fact that the amount of light contributing to display in the transmissive mode comes only from the amount of light passing through the slits formed in the reflective film.
Also, in transflective liquid crystal display devices having other structures, it is difficult to achieve well-balanced display between the reflective mode and the transmissive mode. For example, when conditions for achieving bright, less color-fringing display in the reflective mode are set, the contrast of the display in the transmissive mode is sometimes unsatisfactory; whereas, when other conditions to achieve high-contrast display in the transmissive mode are set, the display in the reflective mode sometimes exhibits color fringing.
The present invention addresses or solves the above and/or other problems, and provides a transflective liquid crystal display device which can be operated in a reflective mode and a transmissive mode, which performs bright display both in the reflective and transmissive modes, and which also performs high-contrast display especially in the transmissive mode. The present invention also provides an electronic apparatus equipped with this liquid crystal display device.
In order to address or achieve the above, a liquid crystal display device according to the present invention, having a structure in which a liquid crystal layer is sandwiched between mutually opposing upper and lower substrates-and display is performed by switching the display mode between a transmissive mode and a reflective mode, includes an upper polarizing layer disposed above the liquid crystal layer; a lower reflective polarizing layer disposed below the liquid crystal layer; a lower polarizing layer disposed below the lower reflective polarizing layer; and an illumination device disposed on the outer surface side of the lower substrate. The lower reflective polarizing layer includes light-transmissive portions formed therein, the transmissive polarization axis of the lower polarizing layer is substantially orthogonal to that of the lower reflective polarizing layer, and the degree of polarization of the lower polarizing layer is greater than that of the lower reflective polarizing layer. When the transmittances of linearly polarized light traveling, in a polarizing layer, parallel and orthogonally to the transmissive polarization axis thereof are respectively defined by T1 and T2, the degree of polarization of the polarizing layer is given by (T1xe2x88x92T2)/(T1+T2)xc3x97100(%) in the present invention.
The liquid crystal display device having the above-mentioned structure enhances display brightness and performs high-contrast display in the transmissive mode, in addition to maintaining display brightness in the reflective mode, whereby bright display can be achieved in both the reflective and transmissive modes. In other words, since the lower reflective polarizing layer having the light-transmissive portions formed therein can be used as a transflective film in the present invention, light emitted from the illumination device is transmitted through the light-transmissive portions so as to contribute to transmissive display. Since the light transmitted through the lower polarizing layer and then reflected from the lower reflective polarizing layer can be recycled, the brightness of the display in the transmissive mode is enhanced. In addition, the liquid crystal display device is constructed such that the transmissive polarization axis of the lower polarizing layer is substantially orthogonal to that of the lower reflective polarizing layer, and the degree of polarization of the lower polarizing layer is greater than that of the lower reflective polarizing layer. Accordingly, for example, light traveling orthogonally to the transmissive polarization axis of the lower polarizing layer (i.e., light traveling parallel to the transmissive polarization axis of the lower reflective polarizing layer) is unlikely transmitted through the lower polarizing layer, and even when the light traveling orthogonally to the transmissive polarization axis of the lower polarizing layer is transmitted therethrough, since the lower reflective polarizing layer has a relatively small degree of polarization, light transmitted through the lower polarizing layer is unlikely transmitted through the lower reflective polarizing layer, thereby reducing or preventing light from escaping. As a result, a liquid crystal display device having enhanced display contrast in the transmissive mode and exhibiting excellent display characteristics can be provided.
In the liquid crystal display device, when the degrees of polarization of the lower polarizing layer and the lower reflective polarizing layer are respectively reduced or defined by Pa and Pr, the condition Paxe2x89xa71.1xc3x97Pr is preferably satisfied. In this case, the light-escaping mentioned above can be more effectively reduced or prevented.
The foregoing lower reflective polarizing layer may be formed by a laminate of dielectric interference films having a prismatic shape. More particularly, the lower reflective polarizing layer may be a so-called three-dimensional photonic crystal layer formed by a substrate having a plurality of grooves periodically formed on the upper surface thereof and by pluralities of two types of layers which are respectively composed of Si (silicon) and SiO2 (silicon dioxide) and which are deposited alternately on the substrate. In this case, components of incident light traveling perpendicularly and parallel to the grooves of the substrate are respectively transmitted through and reflected from the photonic crystal. That is, whether the incident light is transmitted through the dielectric interference films or not depends on the directional relationship between the incident light and the foregoing prism shape.
Also, the foregoing lower reflective polarizing layer may be made from a metal reflective film having a plurality of fine, slit-like apertures formed therein. More particularly, the lower reflective polarizing layer may be formed by a substrate and a highly reflective metal film composed of aluminum or the like, which is formed on the substrate and which has a plurality of slits formed therein at a predetermined pitch. In this case, components of incident light traveling parallel and orthogonally to the longitudinal direction of the slits are respectively reflected from and transmitted through the lower reflective polarizing layer.
An electronic apparatus according to the present invention includes the above-mentioned liquid crystal display device according to the present invention. With this structure, an electronic apparatus equipped with an excellent display unit which performs high-contrast display in the transmissive mode can be achieved.